Electrodeposition of iron



30, 1949. A. E. MATSON ET AL 80,156

ELECTRODEPOS ITION OF IRON Filed Nov. 24, 1944 2 Sheets-Sheet l Aug. 30, 1949. A. E. MATSON ETAL 2,480,156

ELECTRODEPOS ITION OF IRON Filed Nov. 24, 1944 v 2 SheebSSheet 2 ZYW 2 0m Patented Aug. 30, 19453 UNITED STATES FATENT OFFICE ELECTRODEPOSITION OF IRON Application November. 24, 1944, Serial No. 564,935

6 Claims.

This invention relates to the production of a pure, brittle iron suitable for use in powder metallu fgy and particularlyto an electrolytic process forproiducing iron of such brittle character that it may be readily pulverized to particles ofthe required sizes and oisuch dendritic or angular structure as to cause them to intermesh with each other uniformly in the forming dies.

.11; is anobject of our invention to provide a novel and economical method for producing such iron by electrodeposition.

Another object is to provide a process of this general character which includes steps forcontinuously reconditioning the electrolyte with respect to its ferrous and ferric iron content, as well as its pH andtemperature in order to maintain certain critical proportions of constituents in the electrolyte and other beneficial conditions in the deposition cells.

A further and particular object is to provide a method for producing a pure, brittle iron by two stages of electrodeposition in the first stagemf which anodes for use in the second stage are produced and wherein the necessary concentrations of ferrous and ferric salts in the electrolyte for thesecond stage are produced in the cell or cells of the first stage.

Other objects will appear and be more fully pointed out in thefoliowing specification and claims.

Electrodeposited iron as ordinarily produced is too malleable to permit economical grinding. or other pulverization and when ground a large proportion of the particles have had such fiat structures that they tend to stratify in the forming dies with the result that the products termed from the iron powder have had an irregularly laminatedand relatively weak structure. Our improved iron is sufiiciently brittle, having hardness equal to from 4-00 to $500 diamond scale, as deposited at the cathodes to "permit economical crushing. It contains hydrogen and oxygen in amounts which when added together equal less than 1% of the total weight of deposit and less than one half of 1% of other impurities. We crush our :brittle deposit in a ball miller other suitable grinding machine to particles of the.=desired size (usually minus 1G0 mesh) and then drive oil the hydrogen and oxygen by simple annealing treatment in a reducing atmosphere and-at temperatures so low that only slight tritting of the particles results. T-hisproduces a powder is'more than 99.5% pure iron and in which the desired-structure of the particles is retained. In some cases asecondary pulverizi-ng treatment may '2 be necessary to separate the individual particles after the annealing treatment.

Our process may be carried out in .opencells without diaphragms between the anodes and cathodes, As the source ofthe iron, ingot iron plates of suitablethickness, preferably about one inch thick, maybe. used. These plates may containup to .2% of carbon andsubstantial amounts of other impurities. For example, the anode plates may contain 103%. carbon, and manganese, silicon, phosphorous and sulphur totaling togetherapproximately .10% and copper approximately .15%.

Instead of using ingot iron plates as the anodes, according tohourinvention the anodes may-be produced by electrodepositioncarried out in separate cells concurrently with the. electrolysis in the cells producing the brittle deposit. A separate deposition chamber wherein the anodes are insoluble may also be used as .a continuous source of ferric ironto be introducedinto the electrolyte of the main deposition chamber, as morefully hereinafter described.

Our cathode starting sheets in the main .orsecondary-deposition chambers are of such flexible character that the brittle-deposit may be removed therefrom periodically. by flexing. .We prefer to use stainiesssteel cathode sheets having the .de sired flexibility inthe mainv deposition chambers and mild steel sheets to start the cathodes in the primary deposition chambers. Stainless steel sheets containing 18% chromiumand 8% nickel and. .of ld-gauge thickness have been found to be adequately stiff to ,v remain straight in the cells while ,afiordingthe flexibility necessary to permit ready removal of the iron deposit .by flexing. The mild steel cathode starting sheets may contain carboneup to :2% and other impurities as in the caseof-the ingot h'o-nplate for use as soluble anodes in the main deposit-ion chamber.

Y Our electrolyte may he produced .bydissolving scrap iron of low carbon content hydrochloric acid- The concentrated solution of ferrous chloride is preierablydiluted so thatit contains from L to .250 gramsnof iron per liter .of solution. For use in the main-deposition chamber whe e the brittle ironis deposited the electrolyte mustoom tain from l to -.5- grams-of iron-as ieriic iron per liter-of solution and its pH must be maintained below 1.2 and ,preterably from 1 to 1.1 by thead ition of a suflicientxquantity or ;-hydroohlor,ic.acid.

Another important factor in obtaining a brittle deposit of pure iron at the-,cathodesis the control of the temperature the -cell-.so that it does no exceed- 50 :degrees .Cmandis preierably maintained between 20 and 30 degrees C. The temperature may be regulated by continuously circulating the electrolyte through a heat exchanger or otherwise by cooling the walls of the deposition chambers. The use of a heat exchanger located exteriorly of the cell is preferred since it is desirable to maintain the electrolyte in circulation through the cells and this may be accomplished economically by the use of a pump and conduits arranged to continuously withdraw the electrolyte from one end of the cell and to return it to the opposite end after it has been subjected to conditioning treatment, as required. A filter is used in the circuit to remove any solid impurities that may be derived from the impure anodes or other source of iron such as the scrap iron contained in the leach tanks.

In subjecting an electrolyte of the character described to electrolysis for our purposes, it is further important that the rate of flow of current between the electrodes be maintained at a current density of over 25 amperes per square foot and preferably at 30 amperes per square foot. This is a contributing factor in producing a brittle deposit of iron and has the further effect of reducing the power consumption and generally increasing the efficiency of the process.

Referring to the drawings which illustrate diagrammatically suitable flow sheets and apparatus for carrying out our invention:

Figure 1 shows one arrangement of electrolytic cell in electric circuit with a source of direct current and including connections with suitable apparatus for conditioning the electrolyte;

Fig. 2 illustrates a specific procedure wherein primary and secondary deposition cells are employed and the ferric chloride is supplied from the primary cell, and

Fig. 3 illustrates another arrangement of apparatus and procedure wherein the anodes for use in the main cell or cells are produced by electrodeposition in auxiliary cells.

Referring to Fig. 1, the numeral 2 indicates a tank constituting the deposition chamber or cell which may be constructed of suitable material such as rubber, acid-resisting brick, or other material capable of withstanding the corrosive action of the electrolyte contained in the tank. The electrodes comprise a multiplicity of iron anode plates 3 and cathode sheets 4 shown in groups in the tank 2. The cathode sheets extend in suitably spaced, parallel and intermeshing relation to the anode plates of each group, being submerged in an electrolyte of the character hereinbefore described within the tank 2. A source of direct current, indicated by the numeral 5, is connected in circuit with the electrodes by means of conductor cables 6 and I extending to bus bars 8 and 9 respectively. As shown, individual plate connectors 8a extend from the bus bars 8 to the several anode plates 3 of the first group, the cathode sheets 2 of which have connectors Illa extending to a bus bar ll]. Similar connectors lllb connect the anode plates 3 of the second group to the bus bar Ill. The cathode sheets of the second group are in circuit through individual connectors Ila, with a bus bar II and similar connectors llb extend from bar II to the several anode plates of the third group. In a like manner the cathode sheets of the third group are connected to the anode plates of the fourth group through a bus bar 12 and connectors Hat and I2!) while the several cathode sheets of the fourth group have connectors 9a extending to the bus bar 9. It will thus be evident that the several groups of electrodes are connected in series so that an electric current may be caused to flow from the source 5 between the several cathodes and anodes and intervening electrolyte. When the current is caused to flow through this circuit iron is deposited by electrolysis on the cathodes as it is dissolved from the anodes in a manner well known in the art.

As further indicated in Fig. 1, the electrolyte is continuously circulated through the deposition chamber comprising the tank 2 and is reconditioned and then returned for further electrolysis. A pipe l3 conducts the electrolyte from one end of the tank 2 to a pump [4 which is power driven to maintain circulation at the desired rate of flow through the apparatus and conduits presently to be described. From the outlet of the pump a pipe l5 extends to a filter I6 from which a pipe H extends to a heat exchanger l8 having coils wherein the electrolyte is cooled. A cooling medium is supplied to the heat exchanger [8 through an inlet pipe [9 and is discharged through a pipe 20. From the heat exchanger the electrolyte is returned to the tank 2 through a pipe 2|.

A branch 22 of the pipe 21 extends to a source 23 of ferric chloride solution and the flow of this solution to the pipe 2| is under control of a valve 24. Another branch 25 of the pipe 2| supplies hydrochloric acid from a source 26 and the pH of the electrolyte is controlled by adjustment of a valve 21 in the pipe 25. It is necessary to add only a small amount of free acid to the electrolyte to maintain its pH below 1.2 because the desired hydrogen ion concentration is made up in part by the addition of ferric chloride to the electrolyte in an amount equal to less than five grams of ferric iron per liter of solution. By this conditioning treatment for the electrolyte and by causing current to fiow from the source 5 to a density between electrodes of approximately 30 amperes per square foot, we maintain conditions in the deposition chamber which are favorable to a brittle deposit on the cathode sheets 4.

In operation, from time to time as iron is deposited on the stainless steel cathode sheets 4 these sheets are removed from the cell and flexed to dislodge the relatively brittle deposit, after which they may be replaced in the tank to receive a further deposit of pure iron. Separation of the brittle iron coating from the cathode sheets is facilitated if the coating is not allowed to exceed about /32 inch in thickness. The flexing of the iron coated sheets may be performed manually by bending the sheets over a roller or bar or otherwise in a machine designed for the purpose. After repeated use it is sometimes necessary to clean the cathode sheets before returning them to the tank and this may be accomplished by dipping them in dilute hydrochloric acid for a period of from one to five minutes. Cathode sheets of the character described are so durable that they may be used according to our invention almost indefinitely. It will be evident that the anode plates must be replaced by new ones periodically as they are dissolved in the electrolyte.

In Fig. 2 the main deposition cell is indicated by the numeral 28, the anode plates by the numeral 29 and the cathode starting sheets by the numeral 30. Conditions in the cell 23 with respect to temperature, current density, pH of electrolyte and concentration of ferric and ferrous salts in the electrolyte are maintained as hereinbefore described with reference to Fig. l in order to obtain a pure, readily grindable deamuse posit on-the cathodershectsrfl. sitsrfurtheriizidl cated in' Fig. 2, fwciprovide an .nuxliiaryrdcposition 1 chamber comprising a cell .3! :in which are mounted insoluble anode plates 32..and;mild.-:steel or sheet iron cathodes sheets :Asour'ce :34 of direct current 1 is connected .to: bus bars .35 and 56 by branch circuit cablessflandn respectively. The several anodes :32 are connected to .the bus bar 35 andthe cathodes. 33 are. connectedzto arbus bar 39 which is also connected zto .a igroupof the cathodes .30 and ancthcnnndiseparate ;.group of thelanodes :29 in athe-cell .228. Thezanodesifl associated with the :first .mentioned igroup of cathodes :3II are: connecte'rlstc the sbns -bar 36 and the cathodes of: the second. groupxare connected tola bus-bar 45 which is inz-circuitzwith accable extending toithe-sourcesiil oicurrent. LByithis arrangement current :is caused to 'flow .withxthe desired density in thev cells 28 1 and :3 l.

The .electrolyte caused :to snow continuously from 1 the cell 28 through a. conduit .42 to'the cell 3! .and thence through :apipex. ;to a powerdriven pump 44. This pump forces 1 the.electrolyte through a pipe45 to and through aifilter 4 5, then through apipell to a -heatexchanger 43 and from the latter through a pipe.49 vwhich returns it to the-chamber .28. "Asmall amount of hydrochloric acid-is continuously fed into the pipe 149 froma'tank 50 through a pipe-5| under control of a .valve :52. The. concentration: of iron in the electrolyte, when it reaches thew-cells! is equal to approximately 20.0 grams of iron per liter, the greater portlon' of which is intheferrous state although aboutonetotwo gramsper liter remain as ferric iron. In the cell 3| containing the insoluble anodes 32.1ironiis. deposited on the cathode sheets :53 :resulting .in a partial oxidationof the ferrous-.chloridetoaferric chloride and impoverishment :of atheiron in :solution. in sufliclently high rate of how 01; electrolyte through the cell '3! ismaintainedto prevent :deadspots and excessive impoverishment of the solution. For best results not more than 20 .grams ot-lron should be .removed per liter of solution. Conse uently, as withdrawn from cell :51 through the pipe v4i .the electrolyte should contain approximately 5 gramsof ;ferric iron :per liter :of solution. It is then conducted through the :iilter 4.6 and cooler 4.8 and :returned to the .cell :28 through the'pipe 49. .The requisite amount of hydrochloric acid is fed into, the solution through the branch ipe 5i.

In .the cell ZB'the electrolyte is .enriched bythe dissolution of'theanodes zewiththeresult that a portion of its ferric .salt content is reduced to the ferroussalt. Thisloss'of ferricironzmust be .made'up either byzintroducing;asuitable-solution for an external sourcaas .indicatedsinzlrig. 1, or by-electrolysis,,as in the cell.3l, or insome other manner. The iron-deposit on-the cathodes 33 may be allowed to accumulate until these electrodes are-thick .enou hior useas anodesin the cell 28. They may then be replaced by new mild steel or thin iron cathodestartingsheets in the cell Si-and used asaanodesrzsas til-clatter require replacement. It will be understood that the brittle deposit .is removediperiodically from the flexible cathode. sheets 3]! ;for use in iron. powder metallurgy.

In Fig. 3 of the drawings wax-have shown a main de osition cell 52 and auxiliary cells '53, 5.4 and-55 inan arrangement whereby-the anodes ior the cell 52 may be formed by-electrolysis-in the other cells. Each ofithe auxiliary:cells contain a group-f insolubleranodcswt and sheet 6. steel TOIJ'IllOfi rc'athodesxli'l. The main cell 52 has solublei iron anodes .58 and relatively thin, flexible cathodes '59. The electric circuit comprises a sourceiof direct current 550 and. circuit cables 6| and:.2 having. branchess63. and cLextendingrespectively'to bus ibarstiand 66 ofthe cell 52. A bus bar'li'l for'the cell 53 is connected-tothe cable :Bi and a bus .bar 68 for the. cell 55 is connected to the cable 52. :The cell 53 has abus bar 169 connected in series with a bus bar 1090f the .cel1.:54 anda bus bar ii for the cell .154 is connected in series with a bus bar 12 forthe cell 55. Individual 'connectors'extend from the bus lea-r151 to the several anodes 55 of thecell 53. and other individual connectors join the oathodes 5! of the cell 53 with the busbar 69. "In like manner, the several anodes and cathodes of the'cells 54 and 55are connected to the respective bus/bars of these cells so that current maybe caused to flow from the source Ell successively through cells 53,54 and 55. The circuit including the latter .is in parallel with that comprising the cables 63. cell .52 and cable M. In the latter circuit current is caused to how between electrodes 58 and 59 at a current density greater than 25 .amperes per square foot while in the cells 53, 54 and 55 a rate of flow between electrodes may be maintained at approximately 6 tglOz-amneres-per square foot.

The: electrolyte :ior the several-cells '52, 53, 54 and l55 may beformed initiallyby dissolving scrap iron in hydrochloric acid. -Provision-is made'for circulating the solution through these cells and through conditioning apparatus. The flow sheet shown in Fig. 3 includes leach tanks 13 and i4 containing scrap-iron and from which the electrolyte'is caused to'flow through a pipe 15 having branches-for severally supplyingthe cells 53,5 3 and-55 at one end. From the opposite end of each ofthese cells the solution is conducted to a pipe 16 having a branch i7 arranged to supply a powerdriven pump 18. The outlet of this pump comprises a pipe 19 extending to the leach tank '53 from which the solution flows through a pipe to the tank 14. Branch pipe l7 has a valve 8! for controlling the flow of solution to the pump 78. Another branch 82 of the pipe 76 conducts a part of-the electrolyte to apower-driven pump 83 under'control of a valve'84. Fromthe pump 83 electrolyte is caused to How successively through a filter 85 and a heat exchanger 86 and then through, apipe .81 to one end of the cell 52. A branch 88 of the pipe 81 is arranged to'feed hydrochloric acid into the pipe from a tank flilunder controlof a valve 90. The conditioned electrolyte aiterfiowing through-the'cell 5-2is preferably returnedto thescells 53, 54 and 55 through a pipe 91. andthe severalbranchesof pipe 15. By this arrangementof conductingand conditioning an peratus we maintain conditions in the deposition cell52-similar to'those in the=cell .2 of Fig. l and inrtheeell 28-ofFig. 2. The electrolyte in cell 52 containsa total of from to .250 grams of iron perliter of solution of which-from 1 to 5 grams are :ferric iron, the temperatureintthiscell is kept below 5(ldegrees C. and the pH below 1.2. In'the cells 53,..54"and 55 no control of the temperature is necessaryand the pH and ferric iron contentof the :electrolyte are also relatively unimportant tactorswhere afairlypure, soft and malleabledeposit is to-be formed. A pHof from 1 to 35 is suitable.

in operation, the A electrolyte as withdraw from the cells 53, --5':i and 55 through the pipe 15 contains approximately grams of ferric iron per liter of solution. A sufficient quantity of this electrolyte is caused to flow through the branch pipe 82 to the pump 83 which forces it continuously through the filter 85, heat exchanger 85, cell 52 and connecting pipes including pipes 9| and 15, thus returning it to the cells 5.3, 54 and 55. As the anodes 58 dissolve in the electrolyte, iron is deposited in a pure brittle form on the cathodes 59 and is removed therefrom periodically, as hereinbefore described. When the anodes 58 require replacement, new anodes are obtained from the cells 53, 54 and 55 where the cathode sheets 51 are allowed to increase in thickness until they are suitable for use as anodes in the cell 52. It will be evident that a proper balance between the ferric and ferrous iron content of the electrolyte is maintained by successively passing the solution through the leach tanks 73 and M where the ferrous iron is replenished and then through the cells 53, 54 and 55 where the oxidation to ferric iron in a controlled degree takes place.

The presence of ferric chloride in the proportion to ferrous chloride hereinbefore described creates good mechanical conditions for deposition in that it prevents the formation of trees by acting as a depolarizer with respect to hydrogen which tends to adhere to the cathode surfaces and it also assists in making a brittle deposit of the purity required. The free acid present in the electrolyte is also beneficial in that it prevents the formation of hydrolyzed iron.

In the main deposition cells containing the soluble anodes and flexible cathodes, we prefer to use anode plates of approximately one inch thickness and to space the electrodes approximately two inches, center to center, in order to obtain a voltage drop between each pair of electrodes equal to from 2 to 2.1 volts where a current density of approximately 30 amperes per square foot is required.

It is to be understood that the foregoing specific description referring to the diagrammatic illustrations of flow sheets in the several views of the drawings are given by way of illustration and not for the purpose of limiting the present invention. Other arrangements of the electrodes in the circuit will be obvious to those skilled in the art and it will also be evident that in commercial operations a large number of cells may be connected either in parallel or in series in the electric circuit and that other arrangements of conduits and conditioning apparatus may be provided within the scope of the appended claims.

A pure, brittle iron deposit may be produced according to our invention at low cost. The cost of grinding our product is also low as compared with ordinary electrodeposited iron products. Tests show that it has hardness (diamond scale) between 400 and 500 and that it may be pulverized to particles of minus 100 mesh sizes in a ball mill at the rate of approximately 10 to pounds per 100 pounds of balls per hour. After the grinding and annealing treatment a major fraction equal to approximately 95% of all particles have structures of dendritic or other angular shapes adapted to interlock or intermesh with each other in the dies. This powder when cold die pressed under pressures of the order of magnitude of 30 to 50 tons per square inch forms self-sustaining bodies which may be subjected to sintering temperatures to unite the component iron particles in bodies having great and uniform strength throughout. For many purposes these bodies may be formed with such smooth surfaces and so accurately to dimension that no matchin ing or other finishing operation is necessary.

Having described our invention, what we claim as new and desire to protect by Letters Patent is:

l. The method of making electrodeposited iron of pure, brittle character by two stages of electrodeposition which comprises subjecting an electrolyte consisting essentially of ferrous chloride and containing from to 250 grams of iron per liter of solution to electrolysis in a cell having cathodes and insoluble anodes and wherein from 2% to 10% of the iron is oxidized to ferric iron, withdrawing the electrolyte from said cell, cooling at least a portion of it, adding free acid thereto and introducing the electrolyte so conditioned into a second cell containing cathodes and soluble iron anodes produced by electrolysis in the first mentioned-cell, subjecting said solution to electrolysis in the second cell to produce a brittle deposit on the cathodes therein .by maintaining in the second cell an aqueous solution consisting essentially of ferric and ferrous chloride at a total concentration of 150 to 250 grams of iron per liter of solutionof which from 1 to 5 grams is ferric iron, maintaining the temperature of the solution below 50 degrees C., the pH from 1 to 1.2 and the current density of deposition not less than 25 amperes per square foot, withdrawing the electrolyte from the second cell and reintroducing it into the first mentioned cell for further electrolysis therein.

2. The method of making electrodeposited iron of pure, brittle character by two stages of electrodeposition which comprises subjecting an electrolyte consisting essentially of ferrous chloride and containing from 150 to 250 grams of ferrous iron per liter of solution to electrolysis in a cell having cathodes and insoluble anodes and wherein from 2% to 10% of the iron is oxidized to ferric iron, withdrawing the electrolyte from said cell, cooling at least a portion of the electrolyte exteriorly of said cell, adding free acid thereto, introducing the so conditioned electrolyte into a second cell containing cathodes and soluble iron anodes produced by electrolysis in the first mentioned cell, subjecting said solution to electrolysis in the second cell to produce a'brittle deposit on the cathodes therein by maintaining in the second cell an aqueous solution consisting essentially of ferric and ferrous chloride at a total concentration of 150* to 250 grams of iron per liter of solution of which from 1 to 5 grams is ferric iron, maintaining the temperature of the solution below 50 degrees C., the pH from 1 to 1.2 and the current density of deposition not less than 25 amperes per square foot, Withdrawing the electrolyte from the second cell and reintroducing it into the first mentioned cell for further electrolysis therein, continuously withdrawing another portion of the electrolyte from the first mentioned cell and enriching its iron content and returning the enriched electrolyte to the first mentioned cell.

3. The method of making electrodeposited iron of pure, brittle character by two stages of electrodeposition which comprises subjecting an electrolyte consisting essentially of ferrous chloride and containing from 150 to 250 grams of ferrous iron per liter of solution to electrolysis in a cell having cathodes and insoluble anodes and wherein from 2% to 10% of the iron is oxidized to ferric iron, withdrawing the electrolyte from said cell, cooling at least a portion of the electrolyte exteriorly of said cell, adding free acid thereto, introducing the so conditioned electrolyte into a second cell containing cathodes and'soluble' iron anodes pro-.

duced by electrolysis in the first mentioned cell, subjecting said solution to electrolysis in the second cell to produce a brittle deposit on the cathodes therein by maintaining in the second cell an aqueous solution consisting essentiall of ferric and ferrous chloride at a total concentration of 150 to 250 grams of iron per liter of solution of which from 1 to 5 grams is ferric iron, maintaining the temperature of the solution below 50 degrees C., the pH from 1 to 1.2 and the current density of deposition not less than 25 amperes per square foot, withdrawing the electrolyte from the second cell and reintroducing it into the first mentioned cell for further electrolysis therein, continuously withdrawing another portion of the electrolyte from the first mentioned cell, enriching its iron content by passing it through a leach tank containing impure iron and returning the enriched electrolyte to the first mentioned cell.

4. The method of making a substantially pure iron powder which includes the steps of maintaining in a cell a solution containing essentially ferrous and ferric chloride and water at a total concentration of not less than 150 and not greater than 250 grams of iron per liter of solution of which from 1 to 5 grams is ferric iron, subjecting said solution to electrolysis at a current density not less than 25 amperes per square foot between a cathode and a soluble iron anode while maintaining the temperature of the solution below 50 degrees C. and the pH thereof from 1 to 1.2, to thereby produce a brittle, coherent iron deposit containing hardening oxygen and hydrogen compounds removable by annealing and less than 0.5% of other impurities, then pulverizing the brittle deposit to particles of shapes and sizes suitable for compaction in forming dies, and annealing the resulting powder in a reducing atmosphere.

5. The method of making a substantially pure iron powder which includes the steps of maintaining in a cell a solution containing essentially ferrous and ferric chloride and water at a total concentration of not less than 150 and not greater than 250 grams of iron per liter of solution of which from 1 to 5 grams is ferric iron, subjecting said solution to electrolysis at a current density not less than 25 amperes per square foot between a cathode and a soluble iron anode while maintaining the temperature of the solution below 50 degrees C. and the pH thereof from 1 to 1.2, to thereby produce a brittle iron deposit containing hardening oxygen and hydrogen compounds removable by annealing and less than 0.5% of other 10 impurities, then grinding the brittle deposit so formed to particles of minus mesh sizes and suitable for use in powder metallurgy and annealing the powder in a reducing atmosphere and at a low fritting temperature.

6. The method of making a substantially pure iron powder which includes the steps of maintaining in a cell a solution containing essentially ferrous and ferric chloride and Water at a total concentration of not less than and not greater than 250 grams of iron per liter of solution of which from 1 to 5 grams is ferric iron, subjecting said solution to electrolysis at a current density of approximately 30 amperes per square foot between a cathode and a soluble iron anode while maintaining the temperature of the solution below 50 degrees C. and the pH thereof from i to 1.2, to thereby produce a brittle iron deposit containing hardening oxygen and hydrogen com pounds removable by annealing and less than 0.5% of other impurities, then pulverizing the brittle deposit, and annealing the resulting powder in a reducing atmosphere to produce a powder a major fraction of the particles of which have shapes adapted to intermesh when cold die pressed under suitable pressure.

AMEL E. MATSON. HAROLD V. TRASK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Nam-e Date 1,980,381 Cain Nov. 13, 1934 2,157,699 Hardy May 9, 1939 2,223,928 Whitfield et al Dec. 3, 1940 2,287,082 Bauer June 23, 1942 2,385,269 Globus Sept. 18, 1945 FOREIGN PATENTS Number Country Date 10,655 Great Britain 1909 543,137 Great Britain 1942 549,954 Great Britain 1942 813,426 France 1937 OTHER REFERENCES Transactions of the Electrochemical Society, vol. 80 (1941) pages 503, 504.

Transactions of the Electrochemical Society. vol. 84 (1943), pages 305, 306, 308, 309. 

